XML for digital factory automation

A version of XML - the language for data portability - for factory automation could make it simpler to plan engineering workflows and manufacturing processes on computer, E&T explains.

Today, the idea of the digital factory - using digital 3D models and methods to visualise, simulate and commission industrial production systems and processes - is no longer a futuristic vision. In the automotive engineering field, for example, manufacturing cells and their geometric layout are already planned in detail and simulated using computer-aided engineering tools.

The high software cost of these tools is offset by the cost savings from shorter planning cycles, better planning quality, and the fact that it is easier to make changes when necessary. However, further savings will remain unused if these tools do not cover the entire engineering workflow right through to the creation of the schedule in the programmable logic controller (PLC) or in the robot. The same is true if they mainly work sequentially, as a 'tool chain'.

Production planning in most highly developed industries has separated into individual, specialised phases, each of which uses powerful design software tools that remain separate from each other. During engineering, the data is enriched and altered, but while these tools are often used again and again, there is inadequate support for seamless data sharing between them. So there is currently no technical solution that allows the end-to-end, computer-aided planning of manufacturing cells or lines, including the detailed planning, simulation, testing and commissioning of both the geometric layout and the process logic.

Users and suppliers of production equipment are interested in cost-effective and consistent data sharing between all digital planning tools. Today, this consistency only works within the specific system architecture of a particular manufacturer. Even then, it can often only be used for parts of a process chain. There are no open, standardised, and universally accepted data sharing or intermediate formats capable of covering the whole chain.

This is where the AutomationML project comes in. Two years ago, various automation and robotics companies, along with the universities of Karlsruhe and Magdeburg in Germany, set up a joint project to develop a vendor-neutral data format for sharing engineering data. Its goal is to create a common, XML-based language for 3D geometrical descriptions, kinematics and process logic. The V1.0 schema of AutomationML has been published as a free and open standard. It describes a unified, bidirectional data exchange between engineering tools - from the planning stage through to commissioning and the ongoing operation of production plant equipment.

XML for automation

The vision behind the project is to use AutomationML to plan designs for new production machinery more efficiently, without having to invest a lot of effort in data compatibility. If the standard is implemented consistently, the result that users' development work is notably - and durably - easier. It is an ambitious goal, but it also carries a certain measure of risk. The project will only work if the standard is implemented consistently - and its success depends on this one point.

So how would this work in real life? An important phase during production plant engineering is virtual commissioning, which establishes a logical link via open connectivity (OPC) between the real automation system (the PLC) and the virtual mechanical simulation environment. This allows the machine builder to test and validate movements and functional sequences, before the physical machine is even built.

This important step forward is in widespread use today and helps provide measurable cost savings. But it does not yet have any influence on how controls are programmed. All users can do is wait until the simulation environment has been defined and the control program completed, then connect the two components and check the result. In other words, the design processes for simulation and logic are isolated from each other. Although they are developed in parallel, there is no way for them to communicate with each other and correct errors.

So what would happen if users could start testing and comparing before the program and simulation were finished? This would really be a new and exciting scenario

This is the type of model that was announced recently by the partnership between Dassault Systèmes and Rockwell Automation. It allows data and objects to be shared between the tools for mechanical design (Delmia Automation V6) and logic (RSLogix5000 V17), in both directions and at any time. Both tools include the same XML-based export/import object interfaces with the same object structures and domain names. This really speeds up the virtual commissioning process, because users no longer have to delay testing until all the parts have been completed. Instead, they can synchronise and test whatever is finished.

All the selected Smart Devices from the Delmia object library can be synchronised with the corresponding Logix add-on instructions. The objects are sent from the Delmia environment (mechanical) to the Logix environment (process control), where their object attributes and instances are synchronised with the existing library objects there (AOI). The same thing happens in the other direction. Any variations between the object attributes, such as in components' transfer parameters, are immediately detected and registered in the other tool.

For example, let's assume that a mechanical engineer has added an emergency stop button to a control panel. The control programmer will see this change and include it in his or her program. The simulation that follows will be based on object libraries that have already been synchronised.

Revisions and changes

The potential time savings from 3D simulation tend not to be obvious during the initial design of a digital plant model. But there are major advantages once the design is complete because it can easily be reused or modified. The immediate synchronisation of the mechanical and logical objects delivers huge time savings because changes can be implemented far quicker. If commissioning can be coordinated and agreed earlier and faster, the machine can start production considerably sooner. Also, the extra time gained can offset an overly tight schedule, or a risk of late delivery.

There is nothing new about transferring data from a mechanical design tool to a control programming tool for virtual commissioning. Solutions are available that transfer objects and generated program code for various control system families.

However, most of these solutions are currently limited to data transfer in one direction only - from the engineering tool to the controls. The other way involves constraints as well as being time-consuming and risking lost data. For this reason, data transfer is usually only carried out once, at the end of the design process. Rockwell Automation's Logix system takes a new approach with its ability to transfer objects, libraries, and entire projects bidirectionally via an open object interface. This allows engineering tools to share object data in both directions at any time. The XML-based, bidirectional object transfer is used today for virtual commissioning with Delmia Automation.

One can envisage other ways to use the open XML object interface. Using this interface, design tools that generate executable code for the controls will be able to work more effectively with the control programming tool. Any changes created with this tool during commissioning can easily be reused by updating their component library. This will save the current status of the plant machinery. Taking this approach helps reduce the time and effort for adding changes.

The subject of digital manu--facturing spans an enormous area and various specialists have a wide range of differing opinions. However, the scenario described here - virtual commissioning with synchronised simulation and logic objects - demonstrates an important and practical application at the end of the tool chain. In addition, it is easy to see how integrating digital design with digital manufacturing could deliver time and cost savings, making it commercially viable.